Hard alloy and W-based composite carbide powder used as starting material

ABSTRACT

There is disclosed a hard alloy which comprises 5 to 50% by volume of a metallic binder phase comprising at least one element selected from cobalt, nickel and iron as a main component, 0 to 40% by volume of a cubic crystal compound comprising at least one compound selected from a carbide, nitride and mutual solid solution of a metal of Group IVB, VB or VIB of the Periodic Table, and the reminder being hexagonal tungsten carbide and inevitable impurities,  
     wherein at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium is dissolved in the crystal of the hexagonal tungsten carbide as a solid solution in an amount of 0.1 to 3.0% by weight based on the amount of the tungsten carbide.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a hard alloy to be used for cutting tools, wear resistant tools, corrosion resistant and wear resistant parts, etc., and particularly to a hard alloy in which characteristics such as hardness, toughness, strength, wear resistance, fracture resistance, plastic deformation resistance, thermal crack resistance, antioxidation property, corrosion resistance, etc., by adding specific element(s) to crystal of hexagonal tungsten carbide which is a primary hard phase as a solid solution, and to a W-based composite carbide powder which becomes a starting material thereof.

[0003] 2. Prior Art

[0004] A hard alloy produced by mixing, in addition to WC and Co, other powder of carbides such as TiC, TaC, VC, Cr₃C₂, etc., subjecting to molding under pressure, and sintering under heating has been used for various kinds of uses such as cutting tools, wear resistant tools and parts. Also, by adjusting grain size of WC, a Co amount, a kind and amount of a carbide to be added, and the like, alloy characteristics such as hardness, strength, toughness, heat resistance, oxidation resistance, corrosion resistance, etc. required for the respective uses are obtained. With regard to the other carbides to be added, for example, TiC is added to steel cutting tools in which wear due to a reaction or welding becomes a problem, TaC and/or ZrC is/are added to hot-working mold or steel cutting tools in which plastic deformation at high temperatures becomes a problem, VC and/or Cr₃C₂ is/are added to a drill to which hardness and strength are required as a grain growth inhibitor of WC, and Cr₃C₂ and/or Mo₂C is/are added to wear resistant parts in which corrosion becomes a problem.

[0005] However, when one of the alloy characteristics is improved by adding another carbides, there is a problem of antinomy wherein the other alloy characteristics is lowered. For example, when TiC, TaC, ZrC or VC is added, strength or toughness is markedly lowered even when an amount thereof to be added is a little. Also, Cr₃C₂ improves corrosion resistance or oxidation resistance of a binder phase, but WC causes alkali corrosion or preferential oxidation, so that its effect cannot sufficiently be revealed.

[0006] As a measure of the above problems, it has been proposed powder (for example, Japanese Provisional Patent Publication No. Hei. 7-54001, Japanese PCT Provisional Patent Publication No. 2000-512688, Japanese Provisional Patent Publications No. Hei. 10-212165 and No. Hei. 11-236221) for manufacture of a hard alloy to which other carbides are contained in WC powder, or a hard alloy (for example, Japanese Provisional Patent Publications No. Hei. 10-298698, Hei. 11-6025, 2001-81526 and Hei. 10-45414) to which other metals such as Cr, Mn, Re, etc. have been added. The former is intended to prevent from lowering in strength, toughness, etc., while maintaining added effects of the other carbides by dispersing the fine other carbides uniformly, and the latter is intended to strengthen a binder phase by alloying other metals.

[0007] Among the prior art references which relate to powder for producing a hard alloy containing other carbides, in Japanese Provisional Patent Publication No. 7-54001, there is disclosed a preparation method of fine complex carbide powder for preparation of a tungsten carbide-based hard alloy in which mixed powder comprising tungsten oxide, cobalt oxide, carbon, and further carbides of V, Cr, Ta and/or Nb each having an average particle diameter of about 1 μm or lower is subjected to reduction treatment and carbonization treatment both at 700 to 1200° C. In Japanese PCT Provisional Patent Publication No. 2000-512688, there are disclosed powder comprising a transition metal carbide and Group VIII metal and a process for preparing the same, which comprises heating a precursor mixed powder which becomes a metal selected from iron, cobalt and nickel and a transition metal carbide of a metal selected from tungsten, titanium, tantalum, molybdenum, zirconium, hafnium, vanadium, niobium and chromium at 1173 to 1773K (900 to 1500° C.). In Japanese Provisional Patent Publication No. 10-212165, there are disclosed a complex carbide containing a tungsten carbide obtained by heating a mixed powder comprising tungsten oxide and chromium oxide or metallic chromium in hydrogen atmosphere at 700 to 1100° C. to obtain a solid solution or a intermetallic compound, mixing carbon powder thereto, and carbonizing in hydrogen and vacuum at a temperature of 1300 to 1700° C., and 0.5 to 2.0% by weight of metal chromium based on the amount of the tungsten carbide, and a process for preparing the same.

[0008] In complex carbide powders comprising tungsten carbide and transition metal, transition metal carbide, iron-group metal and the like described in these references, transition metal or its carbide is uniformly and finely dispersed, so that when they are used as a hard alloy, characteristics such as hardness, strength, toughness, etc. can be improved but a heating temperature is low so that an amount of the transition metal dissolved in tungsten carbide is extremely little, whereby there is no improvement in characteristics of the tungsten carbide itself. Thus, there is a problem that an antinomy problem possessed by the hard alloy cannot be solved.

[0009] Also, in Japanese Provisional Patent Publication No. Hei. 11-236221, there is disclosed a complex carbonitride material comprising high melting point metals represented by the formula: (M1m, M2n)(CxNy) wherein M1 and M2 are each metal element having a high melting point different from each other among Nb, Mo, Ta and W, m+n=1, 0.0<m<1, x+y≈1, x≦0.99 and y≧0.01, particularly to (W, Mo) (CN). This is to subject a (W, Mo)C solid solution which has conventionally been well known to nitriding synthesis by heating to 500 to 2000° C. in a nitrogen atmosphere at a pressure of 10 atm or higher. The (W, Mo) (CN) powder disclosed in this publication has a wide range of an amount of Mo as a solid solution and when it is employed for a hard alloy, an effect of making particles fine by the nitrogen can be expected. However, when an amount of Mo to be dissolved as a solid solution is large, there are problems that decreases in hardness, strength, wear resistance, plastic deformation property and oxidation resistance are remarkable.

[0010] Among the prior art references relating to hard alloys to which other metal(s) is/are added, in Japanese Provisional Patent Publication No. Hei. 10-298698, there is disclosed a hard alloy comprising 3 to 25% by weight of Co and Ni, 0.1 to 3% by weight of chromium carbide based on the amount of Co and Ni, and the reminder being tungsten carbide and inevitable impurities, and in Japanese Provisional Patent Publication No. Hei. 11-6025, there are disclosed a hard alloy comprising 3 to 25% by weight of Co and Ni in total, 10 to 30% by weight of Cr in terms of chromium carbide based on the amount of Co and Ni, and the reminder being tungsten carbide and inevitable impurities, a coated alloy using the hard alloy as a matrix and coated cutting tools.

[0011] In these chromium-containing hard alloys disclosed in both of the publications, a Cr content, a Co/Ni ratio and grain size of WC are limited to optimum ranges when they are used as cutting tools, and Cr is dissolved in a metal binder phase, but is not dissolved in WC as a solid solution, so that there is a problem that an effect of Cr added cannot sufficiently be shown.

[0012] Also, in Japanese Provisional Patent Publication No. 2001-81526, there is disclosed an iron-based hard alloy comprising a binder phase which comprises Fe containing 0.35 to 3.0% by weight of C, 3.0 to 30.0% by weight of Mn, and 3.0 to 25.0% by weight of Cr. In Japanese Provisional Patent Publication No. Hei. 10-45414, there is disclosed a hard alloy using titanium compound powder as a starting material, which powder has a coated film on the surface thereof, comprising at least one substance selected from the group consisting of Groups 4a, 5a, 6a metal except for titanium, their carbide, nitride and carbonitride, and rhenium metal and iridium metal.

[0013] The hard alloys containing Mn or Re metal disclosed in these publications are to improve strength, toughness, corrosion resistance, heat resistance, etc. of the hard alloy by adding these metals as a solid solution to a metal binder phase, but these metals are not dissolved in WC, so that an effect of adding Mn or Re is little and if an amount of these metals to be added is large, the metal binder phase becomes brittle whereby there are problems that strength and toughness are lowered.

[0014] The present invention is to solve the above-mentioned problems, and specifically, an object of the present invention is to provide a hard alloy in which contradicting alloy characteristics of the hard alloy are simultaneously improved by dissolving specific element(s) such as Ti, Zr, V, Ta, Cr, Mn, etc. into crystalline of WC as a solid solution whereby hardness, toughness, oxidation resistance, corrosion resistance, etc. of the WC itself are improved, and to provide W-based composite carbide powder which becomes a starting material of the hard alloy.

SUMMARY OF THE INVENTION

[0015] The present inventors have studied to improve contradicting characteristics of hard alloy at the same time for a long period of time, and as a result, they have found that to improve characteristics of WC itself is effective, various characteristics of the alloy can be improved when specific element(s) is/are dissolved in the crystal of WC, metals belonging to Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta) or VIB (Cr, Mo) of the Periodic Table (except for W), and Mn and Re are the most effective as the specific element(s), and WC dissolved the specific element(s) therein can be obtained by subjecting a mixed powder of W, C and an oxide of the specific element(s) to heat treatment, whereby they have accomplished the present invention.

[0016] That is, the hard alloy of the present invention comprises 5 to 50% by volume of a metallic binder phase comprising at least one element selected from cobalt, nickel and iron as a main component, 0 to 40% by volume of a cubic crystal compound comprising at least one compound selected from a carbide, nitride and mutual solid solution of a metal of Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta), VIB (Cr, Mo) of the Periodic Table, and the reminder being hexagonal tungsten carbide and inevitable impurities, wherein at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium is dissolved in the crystal of the hexagonal tungsten carbide as a solid solution in an amount of 0.1 to 3.0% by weight based on the amount of the tungsten carbide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The hexagonal tungsten carbide in the hard alloy of the present invention is a material in which at least one of the specific element(s) selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn and Re is dissolved in the crystal of WC as a solid solution. More specifically, there may be mentioned (W,Ti)C, (W,Zr)C, (W,V)C, (W,Ta)C, (W,Cr)C, (W,Mo)C, (W,Re)C, (W,Ti,Mo)C, (W,Zr,Cr)C, (W,V,Cr)C, (W,Nb,Mn)C and (W,Ta,Re)C, which are a complex carbide having the same hexagonal structure as that of WC. An amount of the specific element(s) to be dissolved in WC as a solid solution is defined to be 0.1 to 3.0% by weight, since if it is added in an amount of less than 0.1% by weight, improved effects in hardness, toughness, oxidation resistance, corrosion resistance, etc. are little, whereas Ti, Zr, Hf, V, Nb or Ta is extremely difficult to be dissolved in WC in an amount exceeding 3.0% by weight, and even when Cr, Mo, Mn or Re can be dissolved in WC in an amount exceeding 3.0% by weight, it accompanies with lowering in hardness or oxidation resistance, or formation of brittle sub-carbide material. The amount is preferably 0.3 to 2% by weight.

[0018] Here, the specific element(s) dissolved in WC crystal has slightly different characteristics to be provided to the hard alloy depending on the kind thereof. For example, Ti, Zr, Hf and V improve hardness, wear resistance, welding resistance, oxidation resistance, etc., Nb and Ta improve toughness, fracture resistance, heat resistance, etc., Cr improves toughness, oxidation resistance and corrosion resistance, and Mo, Mn and Re improve hardness, toughness, heat resistance, etc.

[0019] In the hard alloy of the present invention, it is preferred that the specific element(s) is/are at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum, and a content of a cubic crystal compound mentioned hereinbelow is 1% by volume or less, since strength and toughness are particularly high. Also, it is preferred that the specific element(s) is chromium, and 0.1 to 10% by weight of chromium is contained based on the total amount of the hard alloy, since chromium is also dissolved in the metal binder phase as a solid solution, so that improved effects of hardness, toughness, heat resistance, corrosion resistance, oxidation resistance, etc. are more remarkable. Moreover, it is preferred that the specific element(s) is/are manganese and/or rhenium, and 0.1 to 10% by weight of manganese and/or rhenium is/are contained in the total amount of the hard alloy, since it is/they are also dissolved in the binder phase, whereby improved effects of hardness, toughness, heat resistance, etc. are more remarkable.

[0020] The metal binder phase of the hard alloy according to the present invention comprises an alloy containing iron group metal (Fe, Co, Ni) as a main component and 30% by weight or less of W is dissolved therein. More specifically, the binder phase may be mentioned, for example, Co—W alloy, Co—Re alloy, Co—W—Cr alloy, Ni—Mo alloy, Ni—Cr—W alloy, Co—Ni—Cr—W alloy, Fe—Ni—W alloy, Fe—Mo—Cr alloy, Fe—Mn alloy, and the like. An amount of the metal binder phase is defined to be 5 to 50% by volume, since if it is less than 5% by volume, micro pores are remained in the alloy, so that hardness, strength, toughness or fracture resistance is lowered, while if it exceeds 50% by volume, hardness or wear resistance is lowered.

[0021] The cubic crystal compound which is an optional component of the hard alloy according to the present invention may be specifically mentioned, for example, VC, NbC, TaC, (W,Ti)C, (W,Zr)C, (W,Ti,Ta)C, (W,Ti,Re)C, TiN, ZrN, HfN, (W,Ti,Ta)—(C,N), (W,Ti,Mo) (C,N), and the like. Here, the hard alloy of the present invention may contain Cr₇C₃, Mo₂C, etc. which do not belong to the cubic crystal compound with a small amount. If the content of the cubic crystal compound in the hard alloy exceeds 40% by volume, an amount of WC to which the specific element(s) is/are dissolved is relatively lowered, so that an improved effect thereof becomes a little.

[0022] For preparing the hard alloy of the present invention, it is necessary to use powder in which the specific element(s) has/have previously been dissolved in the WC crystal as a starting material. That is, the W-based composite carbide powder of the present invention comprises complex carbide powder which contains tungsten, carbon, and at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium, wherein said complex carbide powder contains 80% by volume or more of hexagonal tungsten carbide, and 0.1 to 3.0% by weight of the specific element(s)is/are dissolved in the crystals of the hexagonal tungsten carbide.

[0023] An amount of the specific element(s) to be dissolved in the W-based composite carbide powder of the present invention is defined to be 0.1 to 3.0% by weight, since if it is less than 0.1% by weight, improved effects on the WC itself such as hardness, toughness, oxidation resistance, corrosion resistance, etc. are low, and it is difficult to dissolve the specific element(s) in an amount exceeding 3.0% by weight in the WC crystal. Here, when the complex carbide of the present invention is represented by the chemical formula, it is a material of (W_(1−x), M_(x))C_(y) wherein x and y satisfy the relationship of 0.002<x<0.06 and 0.95<y<1.00 since the specific element(s) is/are substituted for the W atom in the WC crystal, and taken into the hexagonal crystal lattice. Provided that M represents at least one of the specific elements.

[0024] The W-based composite carbide powder of the present invention comprises WC in which the specific element(s) is/are dissolved as a main component, and a cubic crystal compound into which W is dissolved, and W₂C, Cr₃C₂, Mo₂C or the like into which the specific element(s) is dissolved. If an amount of the WC in which the specific element(s) is/are dissolved is less than 80% by volume, improved effects on hardness, toughness, oxidation resistance, corrosion resistance, etc. due to the specific element(s) dissolved in WC are little in the hard alloy to be produced by using the present products.

[0025] Here, the cubic crystal compound which may be contained in the complex carbide powder comprises W, carbon and/or nitrogen, and at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum. Specific compositions thereof may be mentioned (W_(0.6)Ti_(0.4))C_(0.8), (W_(0.06)Zr_(0.95)) C_(0.75), (W_(0.45)V_(0.55)) C_(0.9), (W_(0.65)Ta_(0.35)) C_(0.9), (W_(0.5)Ti_(0.5)) (C_(0.9)N_(0.1))_(0.95), (W_(0.5)Ti_(0.3)Ta_(0.2))C_(0.9), and the like. These cubic crystal compounds are formed when the specific element(s) is/are added exceeding a limit of an amount capable of being dissolved, and to show added effects of the specific element(s) at the highest level, the presence of the cubic crystal compound is sometimes preferred. However, if an amount thereof becomes 20% by volume or more, it becomes difficult to adjust a ratio of the composition for producing the hard alloy, and in particular, a problem of lowering in strength of the hard alloy arises. Also, W₂C is likely formed when the content of carbon is lower, when the powder is subjected to heat treatment at higher temperatures, when the specific element(s) is Cr or Mo, or the like, but to enlarge an amount of the element(s) to be dissolved, W₂C is rather preferably contained in an amount of up to 5% by volume.

[0026] In the W-based composite carbide powder of the present invention, it is preferred that the WC crystal to which the specific element(s) is/are dissolved has a lattice constant of a axis of a hexagonal crystal lattice of 0.2910 nm or longer and/or a lattice constant of c axis of the same of 0.2840 nm or longer, since dissolution of the specific element(s) in the WC crystal is complete and uniform whereby improved effects of the various kinds of characteristics become maximum.

[0027] The hard alloy of the present invention can be produced by the conventionally employed powder metallurgy method when the W-based composite carbide powder of the present invention is used as a starting material. On the other hand, the W-based composite carbide powder can be obtained, for example, by heating a mixed powder of WC and TiH₂, a mixed powder of W, TiN and carbon, a mixed powder of WO₃, TiO₂ and carbon and the like in a non-oxidative atmosphere or a combined atmosphere of reducing and carburizing atmospheres at high temperatures. Also, when it is produced by the following method and conditions, powder with a much amount of dissolution as well as a uniform dissolution degree and uniform grain size distribution can be produced. That is, the W-based composite carbide powder of the present invention can be produced by subjecting a mixed powder comprising W powder, carbon powder and oxide powder of the specific element(s) each having a grain size of 1 μm or less to heat treatment at 1500 to 2000° C. or so in an inert gas atmosphere or under vacuum. When the heat treatment temperature is higher, an amount of the specific element(s) dissolved in the powder increases but the WC crystals become coarse to cause abnormal grain growth. Also, when Cr or Mn which has a higher vapor pressure is used as the specific element(s), it is necessary to carry out the procedure at a low temperature treatment in which an inert gas is introduced and dissipation thereof shall be prevented.

[0028] In the hard alloy of the present invention, the hexagonal tungsten carbide into which the specific element(s) is/are dissolved, which is in the W-based composite carbide powder used as a starting material has functions of improving hardness, toughness, heat resistance, corrosion resistance, oxidation resistance, etc. of the tungsten carbide itself, and the improved characteristics have functions of improving alloy characteristics or practical characteristics.

EXAMPLE 1

[0029] By using each powder of commercially available W having an average particle size of 0.5 μm, carbon black (hereinafter referred to as “C”) having an average particle size of 0.02 μm, TiO₂, ZrO₂, HfO₂, V₂O₅, Nb₂O₅, Ta₂O₅, Cr₂O₃, MoO₃ and MnO₂ each having an average particle size of 0.05 to 0.2 μm, metal Re having an average particle size of 1.0 μm, and WC (hereinafter referred to as “WC/F”) having an average particle size of 0.5 μm, TiC having an average particle size of 1.2 μm, Mo having an average particle size of 1.1 μm, WC (hereinafter referred to as “WC/C”) having an average particle size of 3.5 μm, each powder was weighed with a formulation shown in Table 1, placed in a pot made of stainless steel with an acetone solvent and balls made of a hard alloy, mixed and pulverized for 24 hours and then dried to obtain respective mixed powders. Then, these mixed powders were each filled in a carbon crusible, and heated after inserting into a vacuum furnace. Heating was carried out under about 20 Pa vacuum until 1200° C., and heating thereafter was carried out under atmosphere and a temperature shown in Table 1 maintaining for 1.0 hour to obtain products of the present invention (present products): PA to PR and Comparative product: complex carbide powders of CA to CH. Provided that Comparative product: CH is not subjected to mixing and heat treatments. TABLE 1 Heated Results of Sample Composition Heated temperature X-ray No. (% by weight) atmosphere (° C.) diffractmetry Present products PA 93.6W—6.2C—0.2TiO₂ Vacuum 1800 WC + W₂C about 10 Pa PB 93.0W—6.3C—0.7TiO₂ Vacuum 1800 WC about 10 Pa PC 91.3W—6.7C—2.0TiO₂ Vacuum 1900 WC + (W, Ti) about 10 Pa C + W₂C PD 88.7W—7.3C—4.0TiO₂ Vacuum 2000 WC + (W, Ti) about 10 Pa C + W₂C PE 92.7W—6.3C—1.0ZrO₂ Vacuum 1900 WC + W₂C about 10 Pa PF 92.8W—6.2C—1.0HfO₂ Vacuum 2000 WC + W₂C about 10 Pa PG 92.5W—6.5C—1.0V₂O₅ Vacuum 1800 WC about 10 Pa PH 92.6W—6.4C—1.0Nb₂O₅ Vacuum 1900 WC + W₂C about 10 Pa PI 92.7W—6.3C—1.0Ta₂O₅ Vacuum 1900 WC + W₂C about 10 Pa PJ 89.0W—7.0C— Vacuum 2000 WC + (W, Ta, 2.0Ta₂O₅—2.0TiO₂ about 10 Pa Ti) C + W₂C PK 91.4W—6.6C—2.0Cr₂O₃ 0.1 MPa Ar 1800 WC + W₂C PL 92.6W—6.4C—1.0Cr₂O₃ 0.1 MPa Ar 1850 WC PM 90.9W—6.6C— 0.1 MPa Ar 1900 WC + 2.0Cr₂O₃—0.5Ta₂O₅ (W, Cr)₂C PN 88.9W—7.1C—4.0MoO₃ Vacuum 1800 WC + W₂C about 10 Pa PO 92.0W—6.5C—1.5MnO₂ 10 kPa Ar 1500 WC + (W, Mn)₂C PP 91.8W—6.6C— 10 kPa Ar 1550 WC 1.0MnO₂—0.5Ta₂O₅ PQ 92.8W—6.2C—1.0Re Vacuum 1800 WC about 10 Pa PR 91.1W—6.3C—2.0Re— 0.1 MPa Ar 1800 WC 0.6Cr₂O₃ Comparative products CA 93.8W—6.2C Vacuum 1700 WC about 10 Pa CB 100.0WC/F Vacuum 1600 WC + W₂C about 10 Pa CC 93.7W—6.2C—0.1TiO₂ Vacuum 1750 WC about 10 Pa CD 99.8WC/F—0.2TiC Vacuum 1800 WC + (W, Ti) about 10 Pa C + W₂C CE 81.2W—8.8C— Vacuum 1900 (W, Ti) C + 10.0TiO₂ about 10 Pa WC + W₂C CF 88.0W—7.0C—5.0Cr₂O₃ 0.1 MPa Ar 1800 WC + (W, Cr)₂C CG 89.0W—6.0C—5.0Mo Vacuum 1800 WC + W₂C about 10 Pa CH 100.0WC/C — — WC

[0030] Complex carbide powders of the thus obtained Present products PA to PR and Comparative products CA to CH were crushed and pulverized, and passed through a sieve of 100 mesh to prepare sample powders for evaluation. With regard to these samples, X-ray diffraction analysis (tube: Cu, tube voltage; 50 kV, tube current; 250 mA) was carried out 10 and components in the powder were identified. The results are also shown in Table 1.

[0031] Next, to the respective sample powders was added 30% by weight of cupper powder (commercially available electrolytic copper powder: 2.5 μm) and the mixture was mixed by using a mortar, and after molding by a mold with a pressure of 2 ton/cm², these samples were heated and sintered under vacuum at 1150° C. for 20 minutes to obtain sample alloys for analyses. Then, these sample alloys were polished by diamond whetstone and subjected to lap processing with a diamond paste having an average particle size of 1 μm, and then, applied to observation and analyses by an electric field radiation type scanning electron microscope.

[0032] First, presence and distribution of WC and particles other than WC (W₂C, cubic crystal compound, etc.) were confirmed by compositional image contrast and element mapping. With regard to WC and cubic crystal compound, compositional analyses were carried out by focusing electronic beam to the center potion of a particle having a relatively large size. Also, a content (% by volume) of the respective particles constituting the respective sample powders was obtained by photographs and an image treatment device. These results are shown in Table 2. Moreover, average particle sizes of WC, W₂C and cubic crystal compounds were obtained. The results are shown in Table 3. TABLE 2 Amount of Composition of powder dissolved (% by volume) Sample element in WC Cubic crystal No. (% by weight) WC W₂C compound Present products PA 0.12Ti 99.0 1.0 O PB 0.42Ti 100.0 0 0 PC 0.82Ti 93.2 2.6  4.2(W_(0.6)Ti_(0.4))C PD 0.87Ti 80.3 3.4 16.3(W_(0.6)Ti_(0.4))C PE 0.73Zr 98.4 1.6 0 PF 0.85Hf 97.1 2.9 0 PG 0.57V 100.0 0 0 PH 0.70Nb 98.0 2.0 0 PI 0.82Ta 99.0 1.0 0 PJ 0.80Ta + 0.54Ti 86.8 3.2 10.0(W_(0.6)Ta_(0.2)Ti_(0.2))C PK 1.37Cr 97.6 2.4 0 PL 0.60Cr 100.0 0 0 PM 1.00Cr + 0.42Ta 99.0 1.0 0 PN 2.73Mo 96.0 4.0 0 PO 0.87Mn 98.7 1.3 0 PP 0.62Mn + 0.37Ta 100.0 0 0 PQ 1.00Re 100.0 0 0 PR 1.75Re + 0.35Cr 100.0 0 0 Comparative products CA 0 100.0 0 0 CB 0 97.9 2.1 0 CC 0.06Ti 100.0 0 0 CD 0.08Ti 98.7 0.4  0.9(W_(0.6)Ti_(0.4))C CE 0.85Ti 39.9 10.4 49.7(W_(0.6)Ti_(0.4))C CF 3.22Cr 92.6 7.4 0 CG 5.00Mo 90.9 9.1 0 CR 0 100.0 0 0

[0033] TABLE 3 Average particle size (μm) Cubic Lattice constants Sample system (nm) No. WC W₂C compound a axis c axis Present products PA 3.1 0.8 — 0.2913 0.2845 PB 2.5 0.6 — 0.2911 0.2844 PC 2.7 0.9 0.9 0.2917 0.2851 PD 3.6 1.3 2.4 0.2915 0.2850 PE 3.0 0.8 — 0.2914 0.2849 PF 7.3 2.0 — 0.2913 0.2846 PG 1.2 0.5 — 0.2911 0.2841 PH 1.8 0.7 — 0.2912 0.2847 PI 2.7 0.8 — 0.2916 0.2850 PJ 3.5 1.1 2.2 0.2919 0.2852 PK 3.1 2.2 — 0.2911 0.2847 PL 2.0 — — 0.2914 0.2847 PM 2.4 1.5 — 0.2912 0.2844 PN 2.4 2.9 — 0.2915 0.2849 PO 2.5 1.8 — 0.2911 0.2850 PP 2.4 — — 0.2919 0.2841 PQ 3.4 — — 0.2914 0.2852 PR 1.7 — — 0.2919 0.2847 Comparative products CA 3.1 0.8 — 0.2905 0.2837 CB 1.3 0.9 — 0.2907 0.2835 CC 2.9 0.8 — 0.2909 0.2841 CD 3.2 1.7 1.4 0.2908 0.2839 CE 2.8 0.8 1.8 0.2917 0.2852 CF 2.2 2.4 — 0.2902 0.2831 CG 3.2 1.4 — 0.2909 0.2855 CH 3.5 1.1 — 0.2906 0.2837

[0034] Next, an interplanar spacing and a lattice spacing were calculated from the position of a peak of WC (2θ=30 to 120°) which was measured by the above-mentioned X-ray diffraction conditions, and lattice constants were obtained with respect to each of a axis and c axis by an extrapolation method. The results are also shown in Table 3.

EXAMPLE 2

[0035] By using complex carbide powders PA, PB, PE, PG, PH, PI, PJ, PK, PL, PM, PO, PP, PQ and PR as well as CA, CB, CD and CH obtained in Example 1, respective powders of W, C and metal Re used in Example 1, and commercially available Co having an average particle size of 1.0 μm, Ni with 1.2 μm, Fe with 1.0 μm, metal Mn with 3.5 μm, and TiC, ZrC, VC, NbC, TaC and Cr₃C₂ each having 1.0 to 1.5 μm, these powders were weighed with a composition shown in Table 4, inserted in a pot made of stainless with an acetone solvent and balls made of hard alloy and pulverized and crushed for 48 hours, and then, dried to obtain respective mixed powders. Here, a formulated carbon amount was adjusted by addition of C or W, so that the alloy became medium carbon alloy (center of a range of a sound phase which does not precipitate free carbon or Co₃W₃C, Ni₂W₄C) after sintering. Then, these powders were filled in a mold, and green compacts having a size of 5.5×9.5×29 mm were produced with a pressure of 196 MPa, placed on a sheet comprising alumina and carbon fiber and heated by inserting into a vacuum atmosphere furnace. Up to 1200° C., the atmosphere was made vacuum of about 20 Pa, and thereafter, heating was carried out in the atmosphere shown in Table 4, and sintering was carried out at 1400° C. for 1.0 hour to obtain hard alloys of Present products 1 to 14 and Comparative products 1 to 14. Incidentally, Present product and Comparative product with the same number were so formulated that the components of the hard alloy and grain size of WC are substantially the same. TABLE 4 Composition Sintering Sample No. (% by weight) atmosphere Present 1 93.0PA—7.0Co Vacuum about 10 Pa Products 2 93.0PB—7.0Co Vacuum about 10 Pa 3 92.92E—0.1C—7.0Co Vacuum about 10 Pa 4 93.0PG—7.0Co Vacuum about 10 Pa 5 92.9PH—0.1C—7.0Co Vacuum about 10 Pa 6 93.0PI—7.0Co Vacuum about 10 Pa 7 92.8PJ—0.2C—7.0Co Vacuum about 10 Pa 8 92.5PK—0.5Cr₃C₂—7.0Co  1 kPa Ar 9 92.0PL—8.0Co  1 kPa Ar 10 91.9PM—0.1C—8.0Co  1 kPa Ar 11 90.0PO—2.0W—8.0Ni 10 kPa Ar 12 89.0PP—3.0W—8.0Ni 10 kPa Ar 13 92.0PQ—8.0Co Vacuum about 10 Pa 14 91.8PR—0.2C—8.0Ee  1 kPa Ar Comparative 1 93.0CD—7.0Co Vacuum about 10 Pa products 2 62.5CA—30.0CB—0.5TiC—7.0Co Vacuum about 10 Pa 3 92.2CA—0.8ZrC—7.0Co Vacuum about 10 Pa 4 92.2CB—0.1C—0.7VC—7.0Co Vacuum about 10 Pa 5 22.1CA—70.0CB—0.1C—0.8NbC— Vacuum about 10 Pa 7.0Co 6 82.2CA—10.0CB—0.8TaC—7.0Co Vacuum about 10 Pa 7 90.0CH—1.GTaC—1.4TiC—7.0Co Vacuum about 10 Pa 8 91.0CA—2.0Cr3C2—7.0Co  1 kPa Ar 9 31.3CA—60.0CB—0.7Cr₃C₂—8.0Co  1 kPa Ar 10 47.9CA—40.0CB—2.2W—0.4TaC—  1 kPa Ar 1.5Cr₃C₂—8.0Co 11 58.1CA—30.0CB—3.0W—0.9Mn— 10 kPa Ar 8.0Ni 12 48.0CA—40.0CB—CB—3.0W—0.4TaC— 10 kPa Ar 0.6Mn—8.0Ni 13 91.1CH—0.9Re—8.0Co Vacuum about 10 Pa 14 19.44CA—60.0CB—0.3C—0.5Cr₃C₂—  1 kPa Ar 1.8Re—8.0Fe

[0036] The resulting hard alloy sample piece was subjected to wet polishing processing with a 230 mesh diamond whetstone to produce a sample with a size of 4.0×8.0×25.0 mm, and transverse-rupture strength (hereinafter abbreviated to as “TRS”) was measured by the JIS method. Also, one surface of the same sample was subjected to lap processing with a diamond past having an average particle size of 0.3 μm, hardness and fracture toughness value K1C (IM method) were measured under a load of 196N using a Vickers indenter. Moreover, micro-structural photograph was taken by an electron microscope with regard to the lap surface of the respective samples, an average particle size of WC and contents of the binder phase and the cubic crystal compound were obtained by using an image treatment device. These results are shown in Table 5. TABLE 5 Amount of Fracture Particle binder Amount of toughness size phase cubic crystal Sample TRS Hardness value of WC (% by compound No. (MPa) (HV) (MPa · m^(½)) (μm) volume) (% by volume) Present products  1 3160 1640 11.6 3.1 11.8 0  2 3050 1670 10.8 2.5 11.5 0.6(W,Ti)C  3 2850 1660 11.3 3.0 11.6 0.2(Zr,W)C  4 2770 1790 8.9 1.2 11.6 0.3VC  5 3210 1710 10.7 1.8 11.6 0.2NbC  6 3140 1650 11.1 2.7 11.7 0.1TaC  7 2540 1680 10.0 3.4 11.1 4.7(W,Ti,Ta)C  8 2910 1630 11.2 3.0 12.6 0  9 2790 1650 10.5 1.9 13.6 0 10 2780 1570 11.2 2.2 14.7 0 11 2840 1610 10.9 2.3 13.7 0 12 2920 1620 10.5 2.1 13.6 0 13 2750 1620 10.6 3.2 13.5 0 14 2790 1630 12.5 2.4 13.7 0 Comparative products  1 2530 1620 11.3 3.2 11.7 0.8(W,Ti)C  2 2310 1640 10.5 2.5 11.5 2.9(W,Ti)C  3 2420 1610 11.1 3.1 11.7 1.7(Zr,W)C  4 2490 1770 8.8 1.2 11.6 1.9VC  5 2170 1690 10.2 1.7 11.7 1.5NbC  6 1980 1630 10.8 2.8 11.8 0.8TaC  7 2410 1630 9.8 3.3 11.0 9.4(W,Ti,Ta)C  8 2760 1590 10.9 3.0 15.1 0  9 2650 1620 10.2 2.0 14.5 0 10 2610 1530 10.7 2.5 15.8 0.5TaC 11 2730 1590 10.5 2.3 15.0 0 12 2840 1610 10.1 2.1 13.8 0.4TaC 13 2750 1610 10.2 3.1 13.9 0 14 2380 1600 12.0 2.3 14.7 0

[0037] The hard alloys produced by the W-based composite carbide powder of the present invention are improved in all of hardness, strength, toughness, etc., as compared with the hard alloy using the conventional high purity WC, when the composition and the WC grain size are made almost the same, and for example, in the hard alloy to which a small amount of TiC or TaC is added, there is a remarkable effect that strength is highly improved. 

1. A hard alloy which comprises 5 to 50% by volume of a metallic binder phase comprising at least one element selected from cobalt, nickel and iron as a main component, 0 to 40% by volume of a cubic crystal compound comprising at least one compound selected from a carbide, nitride and mutual solid solution of a metal of Group IVB, VB or VIB of the Periodic Table, and the reminder being hexagonal tungsten carbide and inevitable impurities, wherein at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium is dissolved in the crystal of the hexagonal tungsten carbide as a solid solution in an amount of 0.1 to 3.0% by weight based on the amount of the tungsten carbide.
 2. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of titanium, zirconium, hafnium and vanadium.
 3. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of niobium and tantalum.
 4. The hard alloy according to claim 1, wherein the specific element(s) is chromium.
 5. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of molybdenum, manganese and rhenium.
 6. The hard alloy according to claim 1, wherein the specific element(s) is at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum, and the cubic crystal compound is contained in an amount of 1% by volume or less.
 7. The hard alloy according to claim 1, wherein the specific element(s) is chromium, and chromium is contained in an amount of 0.1 to 10% by weight based on the total amount of the hard alloy.
 8. The hard alloy according to claim 1, wherein the specific element(s) is at least one of manganese and rhenium, and the at least one of manganese and rhenium is contained in an amount of 0.1 to 10% by weight based on the total amount of the hard alloy.
 9. A tungsten-based complex carbide powder which comprises a complex carbide powder containing tungsten, carbon, and at least one specific element(s) selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, manganese and rhenium, wherein the complex carbide powder contains 80% by volume or more of hexagonal tungsten carbide, and the specific element(s) is dissolved in the crystal of the hexagonal tungsten carbide in an amount of 0.1 to 3.0% by weight.
 10. The tungsten-based complex carbide powder according to claim 9, wherein the powder contains particles of a cubic crystal compound comprising tungsten, at least one of carbon and nitrogen, and at least one selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum in an amount of less than 20% by volume.
 11. The tungsten-based complex carbide powder according to claim 9, wherein the crystal of the hexagonal tungsten carbide has at least one of a lattice constant of a axis of 0.2910 nm or longer and a lattice constant of c axis of 0.2840 nm or longer. 